The overall objective of this proposal is to characterize the response of skeletal muscle to non-neurogenic atrophy. This will be accomplished by determining some fundamental physiological, biochemical, and histochemical properties of skeletal muscle atrophy as induced by 1) unilateral skeletal fixation, 2) chronic steroid treatment, and 3) a combination of steroid treatment and several levels and kinds of physical activity. The current objectives will be to quantify changes that occur in the EMG of slow and fast muscles as a result of immobilization and steroid treatment; to initiate experiments on the steroid treatment of rats that are exercised. BIBLIOGRAPHIC REFERENCES: Gardner, G.W., Edgerton, V.R., Senewiratne, B., Barnard, R.J., and Ohira, Y. Physical work capacity, and metabolic stress in subjects with iron deficiency anemia. Amer. J. Clin. Nutr. 1977, in press. Smith, J.L., Edgerton, V.R., Betts, B., and Collatos, T.C. EMG of slow and fast ankle extensors of cat during posture, locomotion and jumping. J. Neurophysiol., 1977, in press.